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Metamaterial has received widespread research in the fields of electromagnetic stealth due to its characteristics of strong resonance and flexible designability. However, a lack of a comprehensive understanding of the internal physical mechanism still imposes certain limitations on broadband absorption designs. Hence, this work proposes a new strategy for the broadening of the working frequency band of metamaterial absorbers by constructing local-chiral features to regulate the amplitude and phase information. The absorber consists of staggered cut-wire metal patterns with lumped resistors placed at the center position determined by characteristic mode analysis. Combining the modal significance, equivalent circuit, surface current, electric field distribution, and symmetry model theory, the working mechanism for wideband absorption performance has been analyzed in detail. The experimental results are in good agreement with the simulation results; the absorption rate exceeds 82% in the frequency range of 4.5-11.7 GHz and surpasses about 90% in the frequency range of 4.7-10.8 GHz under transverse electric (TE) or transverse-magnetic (TM) polarizations. Compared to the case without chiral features, the proposed design can achieve a 28% increase in operating bandwidth. The proposed design method is applicable for the optimization of various typical dipole-type metamaterial absorbers and provides a novel strategy for future wideband metamaterial absorption.

It has been accepted that the uniform distribution of magnetic metal particles is beneficial to microwave absorption, while why the homogeneous magnetic particles on the dielectric substrate improve the electromagnetic loss is still unclear. Herein, metal Ni nanoparticles, two-dimensional (2D) basalt/scattered Ni, and basalt/uniform Ni microflakes are obtained through a pretreatment and electroless deposition process. In comparison to Ni nanoparticles and basalt/scattered Ni, the basalt/Ni microflakes with largely uniform and compact Ni nanolayers on basalt, breaking the percolation limit, are favorable for enhanced electromagnetic attenuation. The Ni nanolayers are convenient for construction of a microscale conductive net and migration of an electron. The 2D heterostructures constructed by basalt substrates and decorated Ni layers boost multiple scattering absorption and promote interfacial polarization. Meanwhile, exposed Ni does not inhibit magnetic resonance, enabling strong magnetic coupling. Consequently, the basalt/Ni microflakes with uniform Ni nanolayers demonstrate better microwave absorption with a minimum reflection loss of -30 dB and an effective absorption bandwidth of 3 GHz at 1 mm. This work shows that the uniform and compact magnetic metal nanolayers are effective in improving the dielectric loss and magnetic loss simultaneously to achieve the high-performance microwave absorption.